This is not a trick question. This is a real math problem so don't say that a bus has no legs. There is no bus driver either so don't worry about counting those legs! That's all the help you get.

There are 7 girls in a bus.

Each girl has 7 backpacks.

In each backpack, there are 7 big cats.

For every big cat there are 7 little cats.

Question: How many legs are there in the bus?

for the record, i know it doesn't explicitly say that the backpacks are on the bus with the girls so i'm telling you that now